The present invention relates to an oil seal assembly for forming a liquid tight seal between a wall of a stationary housing and a rotatable shaft extending through the wall of the housing to prevent a fluid from leaking from the inside to the outside of the housing along the shaft. More particularly, the invention is concerned with an oil seal assembly of the kind described above, provided with a backup ring for backing up the lip neck portion of an elastic seal ring.
In the field of machines having a shaft rotatably mounted in a housing to project outwardly from the housing through a housing wall, it is well known to use an oil seal assembly for preventing any leak of an internal fluid to the outside of the machine through the gap between the shaft and the housing wall. Usually, the oil seal assembly is provided with a backup ring for backing up a seal member.
An oil seal assembly having a backup ring is shown, for example, in Japanese Patent Publication No. 8338/1982. In this oil seal assembly, the backup ring is constituted by a part of a metallic ring having a substantially U-shaped cross-section and composed of two segments. More specifically, one of the two segments of the metallic ring is wholly coated with an adhesive and is bonded by firing to an elastic seal ring having a lip during the forming of the elastic seal ring, while the other segment is not bonded so that the elastic seal ring is freed from the metallic ring only at the portion thereof around the lip. In this type of oil seal assembly, however, it is necessary to machine the outer peripheral surface of the non-bonded segment in exact conformity with the inner peripheral configuration of the lip neck portion of the elastic seal ring. This machining is considerably difficult and troublesome to conduct. In addition, the rubber used as the material of the elastic seal ring tends to flow into the inner periphery of the backup ring to form burrs, by the pressure applied thereto during the formation of the elastic seal ring together with the backup ring.
On the other hand, Japanese Utility Model Publication No. 15919/1959 discloses an oil seal assembly with a backup ring in which the backup ring is fitted to the elastic seal ring after the formation of the latter. In this case, however, the productivity is impractically low due to the necessity of the fitting work. In addition, it is difficult to obtain a close fit between the backup ring and the inner peripheral surface of the lip neck portion of the elastic seal ring and, hence, the durability of the elastic seal ring is impaired disadvantageously. It is to be pointed out also that the backup ring is pressed onto the rotating shaft when a pressure is applied to the seal so that the backup ring is undesirably rotated together with the shaft to damage the oil seal assembly. Furthermore, the backup ring is required to have an antidust lip for preventing dust from coming into the housing.